Fuel combusting method with co2 capture

ABSTRACT

A method for capturing emissions from a fuel combustion process comprising: providing a fuel to a combustor on a gas turbine, providing an oxidant to the combustor, combusting the fuel and the oxidant in the combustor to produce an exhaust gas, passing at least a portion of the exhaust gas to one or more catalyst beds. The one or more catalyst beds promote a reaction which consumes CO and produces CO 2  and adsorb CO 2 . Pressure at the catalyst beds is reduced by outputting a blow down stream from the catalyst beds and then CO 2  is purged from the one or more catalyst beds with a regenerant stream to create a product stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser. No. 62/256,366 filed on Nov. 17, 2015, herein incorporated by reference in its entirety.

FIELD

The present disclosure relates generally to low-emission power generation systems. More particularly, the present disclosure relates to systems and methods for changing the composition of components in exhaust gases from gas turbine systems.

BACKGROUND

This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.

The combustion of fuel within a combustor, e.g., integrated with a gas turbine, can be controlled by monitoring the temperature of the exhaust gas. Under full load conditions, typical gas turbines adjust the amount of fuel introduced to a number of combustors in order to reach a desired combustion gas or exhaust gas temperature. Conventional combustion turbines control the oxidant introduced to the combustors using inlet guide vanes. Under partial load conditions, the amount of oxidant introduced to the combustor is reduced and the amount of fuel introduced is again controlled to reach the desired exhaust gas temperature. Further, at partial load, the efficiency of gas turbines drops because the ability to reduce the amount of oxidant is limited by the inlet guide vanes, which are only capable of slightly reducing the flow of oxidant. Further, the oxidant remains at a constant lower flow rate when the inlet guide vanes are in their flow restricting position. The efficiency of the gas turbine then drops when it is at lower power production because to make that amount of power with that mass flow a lower expander inlet temperature is required. Moreover, existing oxidant inlet control devices may not allow fine flow rate control and may introduce large pressure drops with any restriction on the oxidant flow. With either of these approaches to oxidant control, there are potential problems with lean blow out at partial load or reduced pressure operations.

Controlling the amount of oxidant introduced to the combustor can be desirable when an objective is to capture carbon dioxide (CO₂) from the exhaust gas. Current carbon dioxide capture technology is expensive due to several reasons. One reason is the low pressure and low concentration of carbon dioxide in the exhaust gas. The carbon dioxide concentration, however, can be significantly increased from about 4% to greater than 10% by operating the combustion process under substantially stoichiometric conditions. Further, a portion of the exhaust gas may be recycled to the combustor as a diluent in order to control the temperature of the gas within the combustor and of the exhaust gas. Also, any unused oxygen in the exhaust gas may be a contaminant in the captured carbon dioxide, restricting the type of solvents that can be utilized for the capture of carbon dioxide.

In many systems, an oxidant flow rate may be reduced by altering the operation of a separate oxidant system. For example, an independent oxidant compressor may be throttled back to a slower operating speed thereby providing a decreased oxidant flow rate. However, the reduction in compressor operating speed generally decreases the efficiency of the compressor. Additionally, throttling the compressor may reduce the pressure of the oxidant entering the combustor. In contrast, if the oxidant is provided by the compressor section of the gas turbine, reducing the speed is not a variable that is controllable during power generation. Large gas turbines that are used to produce 60 cycle power are generally run at 3600 rpm. Similarly, to produce 50 cycle power the gas turbine is often run at 3000 rpm. In conventional gas turbine combustor operations the flow of oxidant into the combustor may not warrant significant control because the excess oxidant is used as coolant in the combustion chamber to control the combustion conditions and the temperature of the exhaust gas. A number of studies have been performed to determine techniques for controlling combustion processes in gas turbines.

International Patent Application Publication No. W0/2010/044958 by Mittricker et al. discloses methods and systems for controlling the products of combustion, for example, in a gas turbine system. One embodiment includes a combustion control system having an oxygenation stream substantially comprising oxygen and CO₂ and having an oxygen to CO₂ ratio, then mixing the oxygenation stream with a combustion fuel stream and combusting in a combustor to generate a combustion products stream having a temperature and a composition detected by a temperature sensor and an oxygen analyzer, respectively. The data from the sensors are used to control the flow and composition of the oxygenation and combustion fuel streams. The system may also include a gas turbine with an expander and having a load and a load controller in a feedback arrangement.

International Patent Application Publication No. W0/2009/120779 by Mittricker et al. discloses systems and methods for low emission power generation and hydrocarbon recovery. One system includes integrated pressure maintenance and miscible flood systems with low emission power generation. Another system provides for low emission power generation, carbon sequestration, enhanced oil recovery (EOR), or carbon dioxide sales using a hot gas expander and external combustor. Another system provides for low emission power generation using a gas power turbine to compress air in the inlet compressor and generate power using hot carbon dioxide laden gas in the expander.

U.S. Pat. No. 4,858,428 to Paul discloses an advanced integrated propulsion system with total optimized cycle for gas turbine. Paul discloses a gas turbine system with integrated high and low pressure circuits having a power transmission for extracting work from one of the circuits, the volume of air and fuel to the respective circuits being varied according to the power demand monitored by a microprocessor. The turbine system has a low pressure compressor and a staged high pressure compressor with a combustion chamber and high pressure turbine associated with the high pressure compressor. A combustion chamber and a low pressure turbine are associated with the low pressure compressor, the low pressure turbine being staged with the high pressure turbine to additionally receive gases expended from the high pressure turbine and a microprocessor to regulate air and gas flows between the compressor and turbine components in the turbine system.

U.S. Pat. No. 4,271,664 to Earnest discloses a turbine engine with exhaust gas recirculation. The engine has a main power turbine operating on an open-loop Brayton cycle. The air supply to the main power turbine is furnished by a compressor independently driven by the turbine of a closed-loop Rankine cycle which derives heat energy from the exhaust of the Brayton turbine. A portion of the exhaust gas is recirculated into the compressor inlet during part-load operation.

U.S. Patent Application Publication No. 2009/0064653 by Hagen et al. discloses partial load combustion cycles. The part load method controls delivery of diluent fluid, fuel fluid, and oxidant fluid in thermodynamic cycles using diluent to increase the turbine inlet temperature and thermal efficiency in part load operation above that obtained by relevant art part load operation of Brayton cycles, fogged Brayton cycles, or cycles operating with some steam delivery, or with maximum steam delivery.

U.S. Pat. No. 5,355,668 to Weil et al. discloses a catalyst-bearing component of a gas turbine engine. Catalytic materials are formed on components in the gas flow path of the engine, reducing emissions of carbon monoxide and unburned hydrocarbons. The catalytic materials are selected from the noble metals and transition metal oxides. The portions of the gas t1ow path where such materials are applied can include the combustor, the turbine, and the exhaust system. The catalytic coating can be applied in conjunction with a thermal barrier coating system interposed between a substrate component and the catalytic coating.

While some past efforts to control the oxidant flow rate have implemented oxidant inlet control devices, such systems disclosed a control of all of the combustors together, failing to account for differences between combustors. Further, the systems were limited in their ability to finely tune the oxidant flow rate. As a result, the concentration of certain gases in the exhaust was higher than desirable.

SUMMARY

Certain embodiments of the present invention are directed to methods for capturing emissions from a fuel combustion process comprising: providing a fuel to a combustor on a gas turbine, providing an oxidant to the combustor, combusting the fuel and the oxidant in the combustor to produce an exhaust gas, and passing at least a portion of the exhaust gas to one or more catalyst beds. The one or more catalyst beds promote a reaction which consumes CO and produces CO₂ and adsorb CO₂. After passing the exhaust gas to the catalyst beds, the pressure at the catalyst beds is reduced by outputting a blow down stream from the catalyst beds and CO₂ is purged from the one or more catalyst beds with a regenerant stream to create a recovery stream.

The invention may be embodied by numerous other devices and methods. The description provided herein, when taken in conjunction with the annexed drawings, discloses examples of the invention. Other embodiments, which incorporate some or all steps as taught herein, are also possible.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings, which form a part of this disclosure:

FIG. 1 schematically shows a diagram of a gas turbine system that includes a gas turbine;

FIG. 2 schematically shows a gas turbine system that includes an HRSG and catalyst beds on the exhaust stream from the expander exhaust section;

FIG. 3 schematically shows a diagram of a configuration of catalyst beds and non-catalyst beds on the exhaust stream from the turbine and HRSG;

FIG. 4A and FIG. 4B show graphical depictions of a simulation showing the relationship between the concentration of oxygen and carbon monoxide;

FIG. 5 shows a block diagram of a method for adjusting fuel and oxidant levels to the combustors based on readings from an array of sensors;

FIG. 6 shows a block diagram of a plant control system that may be used to control the oxidant and fuel to the combustors in a gas turbine engine; and

FIG. 7 shows a schematic of a simulated gas turbine system that illustrates the use of two catalyst beds in a HRSG to reduce the concentration of selected components in the exhaust stream.

DETAILED DESCRIPTION

In the following detailed description section, specific embodiments of the present techniques are described. However, to the extent that the following description is specific to a particular embodiment or a particular use of the present techniques, this is intended to be for exemplary purposes only and simply provides a description of the exemplary embodiments. Accordingly, the techniques are not limited to the specific embodiments described below, but rather, include all alternatives, modifications, and equivalents falling within the true spirit and scope of the appended claims.

At the outset, for ease of reference, certain terms used in this application and their meanings as used in this context are set forth. To the extent a term used herein is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Further, the present techniques are not limited by the usage of the terms shown below, as all equivalents, synonyms, new developments, and terms or techniques that serve the same or a similar purpose are considered to be within the scope of the present claims.

A “combined cycle power plant” uses both steam and gas turbines to generate power. The gas turbine operates in an open or semi-open Brayton cycle, and the steam turbine operates in a Rankine cycle powered by the heat from the gas turbine. These combined cycle gas/steam power plants generally have a higher energy conversion efficiency than gas or steam only plants. A combined cycle plant's efficiencies can be as high as 50% to 60%. The higher combined cycle efficiencies result from synergistic utilization of a combination of the gas turbine with the steam turbine. Typically, combined cycle power plants utilize heat from the gas turbine exhaust to boil water to generate steam. The boilers in typical combined cycle plants can be referred to as heat recovery steam generator (HRSG). The steam generated is utilized to power a steam turbine in the combined cycle plant. The gas turbine and the steam turbine can be utilized to separately power independent generators, or in the alternative, the steam turbine can be combined with the gas turbine to jointly drive a single generator via a common drive shaft.

A diluent is a gas that is primarily used to reduce the combustor temperatures that result from the combustion of a fuel and oxidant. A diluent may be used to lower the concentration of oxidant or fuel (or both) that is fed to a gas turbine and/or to dilute the products of combustion. The diluent may be an excess of nitrogen, CO₂, combustion exhaust, or any number of other gases. In embodiments, a diluent may also provide cooling to a combustor and/or other parts of the gas turbine.

As used herein, a “compressor” includes any type of equipment designed to increase the pressure of a working fluid, and includes any one type or combination of similar or different types of compression equipment. A compressor may also include auxiliary equipment associated with the compressor, such as motors, and drive systems, among others. The compressor may utilize one or more compression stages, for example, in series. Illustrative compressors may include, but are not limited to, positive displacement types, such as reciprocating and rotary compressors for example, and dynamic types, such as centrifugal and axial flow compressors, for example. For example, a compressor may be a first stage in a gas turbine engine, as discussed in further detail below.

A “control system” typically comprises one or more physical system components employing logic circuits that cooperate to achieve a set of common process results. In an operation of a gas turbine engine, the objectives can be to achieve a particular exhaust composition and temperature. The control system can be designed to reliably control the physical system components in the presence of external disturbances, variations among physical components due to manufacturing tolerances, and changes in inputted set-point values for controlled output values. Control systems usually have at least one measuring device, which provides a reading of a process variable, which can be fed to a controller, which then can provide a control signal to an actuator, which then drives a final control element acting on, for example, an oxidant stream. The control system can be designed to remain stable and avoid oscillations within a range of specific operating conditions. A well-designed control system can significantly reduce the need for human intervention, even during upset conditions in an operating process.

An “equivalence ratio” refers to the mass ratio of fuel to oxygen entering a combustor divided by the mass ratio of fuel to oxygen when the ratio is stoichiometric. A perfect combustion of fuel and oxygen to form CO₂ and water would have an equivalence ratio of 1. A too lean mixture, e.g., having more oxygen than fuel, would provide an equivalence ratio less than 1, while a too rich mixture, e.g., having more fuel than oxygen, would provide an equivalence ratio greater than 1.

A “fuel” includes any number of hydrocarbons that may be combusted with an

oxidant to power a gas turbine. Such hydrocarbons may include natural gas, treated natural gas, kerosene, gasoline, or any number of other natural or synthetic hydrocarbons.

A “gas turbine” engine operates on the Brayton cycle. If the exhaust gas is vented, this is termed an open Brayton cycle, while recycling at least a portion of the exhaust gas gives a semi-open Brayton cycle. In a semi-open Brayton cycle, at least fuel and oxidant are added to the system to support internal combustion and a portion of the products of combustion are vented or extracted. In a closed Brayton cycle, all of the exhaust is recycled and none is vented or extracted and heat is added to the system by external combustion or another means. As used herein, a gas turbine typically includes a compressor section, a number of combustors, and a turbine expander section. The compressor may be used to compress an oxidant, which is mixed with a fuel and channeled to the combustors. The mixture of fuel and oxidant is then ignited to generate hot combustion gases. The combustion gases are channeled to the turbine expander section which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to power a load. In embodiments discussed herein, the oxidant may be provided to the combustors by an external compressor, which may or may not be mechanically linked to the shaft of the gas turbine engine. Further, in embodiments, the compressor section may be used to compress a diluent, such as recycled exhaust gases, which may be fed to the combustors as a coolant.

A “heat recovery steam generator” or HRSG is a heat exchanger or boiler that recovers heat from a hot gas stream. It produces steam that can be used in a process or used to drive a steam turbine. A common application for an HRSG is in a combined-cycle power plant, where hot exhaust from a gas turbine is fed to the HRSG to generate steam which in turn drives a steam turbine. This combination produces electricity more efficiently than either the gas turbine or steam turbine alone. As used herein, an HRSG may include any number of heat recovery units in addition to, or instead of, an HRSG by itself.

A “hydrocarbon” is an organic compound that primarily includes the elements hydrogen and carbon, although nitrogen, sulfur, oxygen, metals, or any number of other elements may be present in small amounts. As used herein, hydrocarbons generally refer to components found in raw natural gas, such as CH₄, C₂H₂, C₂H₄, C₂H₆, C₃ isomers, C₄ isomers, benzene, and the like.

An “oxidant” is a gas mixture that can be flowed into the combustors of a gas turbine engine to combust a fuel. As used herein, the oxidant may be oxygen mixed with any number of other gases as diluents, including CO₂, N₂, air, combustion exhaust, and the like.

A “sensor” refers to any device that can detect, determine, monitor, record, or otherwise sense the absolute value of or a change in a physical quantity. A sensor as described herein can be used to measure physical quantities including, temperature, pressure, O₂ concentration, CO concentration, CO₂ concentration, flow rate, acoustic data, vibration data, chemical concentration, valve positions, or any other physical data.

“Pressure” is the force exerted per unit area by the gas on the walls of the volume. Pressure can be shown as pounds per square inch (psi). “Atmospheric pressure” refers to the local pressure of the air. “Absolute pressure” (psia) refers to the sum of the atmospheric pressure (14.7 psia at standard conditions) plus the gage pressure (psi g). “Gauge pressure” (psig) refers to the pressure measured by a gauge, which indicates only the pressure exceeding the local atmospheric pressure (i.e., a gauge pressure of 0 psig corresponds to an absolute pressure of 14.7 psia). The term “vapor pressure” has the usual thermodynamic meaning. For a pure component in an enclosed system at a given pressure, the component vapor pressure is essentially equal to the total pressure in the system.

“Substantial” when used in reference to a quantity or amount of a material, or a specific characteristic thereof, refers to an amount that is sufficient to provide an effect that the material or characteristic was intended to provide. The exact degree of deviation allowable may in some cases depend on the specific context.

Overview

Embodiments of the present invention provide a system and a method for consuming carbon monoxide generated in the combustion in a gas turbine engine. This is performed by a water gas shift reaction, for example, in a catalyst bed located in a heat-recovery steam generator (HRSG). The water gas shift reaction is a chemical reaction between carbon monoxide and water vapor that forms carbon dioxide and hydrogen as products. The water-gas shift reaction is a predominant reaction given the relatively large quantity of water vapor present in the exhaust from the gas turbine. In some embodiments, such as in a stoichiometric exhaust gas recirculation (SEGR) gas turbine, the exhaust is a recirculated low oxygen content gas stream, which is used at least as a coolant gas in the combustors. Typically, water vapor content of more than 10 volume percent (>100k parts per million volume, ppmv) is present in the recirculated low oxygen content gas stream while oxygen, carbon monoxide and hydrogen are of the order of 1000 to 5000 ppmv. As a result, the water-gas shift reaction is able to consume residual carbon monoxide plus a similar quantity of water vapor to create carbon dioxide and hydrogen at a higher conversion efficiency than the competing oxidation reactions. The resulting low CO content product gas may comprise as little as 1 or 2 ppm CO.

A moderate conversion efficiency may be acceptable, since the high concentration of water vapor relative to the concentration of carbon monoxide will still tend to force a high conversion. The catalyst bed may be located in a moderate temperature zone of the HRSG, e.g., in a zone of about 150° C. to about 250° C. or 100° C. to 400° C., since lower temperature zones of the HRSG are well suited for catalyst systems designed for a water-gas shift reaction. Hydrogen formed in the reaction will likely have a very low conversion efficiency to oxidization to water vapor. Accordingly, the hydrogen may be recirculated within the recirculated low oxygen content gas stream to the compressor section of the SEGR gas turbine and then may either be extracted as part of the product stream, used as part of the sealing and cooling stream of the gas turbine hot gas path or transit to the combustor where this hydrogen should be largely oxidized within the combustors. The hydrogen part extracted as part of the product stream should be easily oxidized to water vapor within the first oxidation catalyst unit included within the product extraction circuit. Overall, this arrangement should provide improved conversion efficiency.

In some embodiments described herein, an oxidation catalyst is used in a hot zone of the HRSG to oxidize carbon monoxide, hydrogen, and unburned hydrocarbons with residual oxygen from the gas turbine exhaust, forming carbon dioxide and water. A moderate oxidizing conversion efficiency may be accepted in order to provide a low pressure drop across a catalyst bed.

Sensors may be placed in the exhaust gas, the product gas, or both to adjust the combustion conditions to control the amount of CO, oxygen or other contaminants in the exhaust gas. For example, the sensors may be located in a ring on an expander exhaust, an inlet to the catalyst bed, an outlet from a catalyst bed, or any combination. The sensors may include lambda sensors, oxygen sensors, carbon monoxide sensors, and temperature sensors, among others. Further, combinations of different types of sensors may be used to provide further information.

In some embodiments, multiple sensors may be used to adjust the conditions in individual combustors on the gas turbine. The sensors may not have a one-to-one relationship to particular combustors, but may be influenced by a particular combustor. The response of various sensors may be related back to a particular combustor, for example, using sum and difference algorithms that may be based on swirl charts. Swirl charts relate patterns of exhaust flow in an expander to combustors that may have contributed to the exhaust flow at that point.

The use of individually controlled combustors may increase the burn efficiency of a gas turbine engine, e.g., making the burn closer to a one-to-one equivalence ratio. Such improvements in efficiency may lower 0 2, unburned hydrocarbons, and carbon monoxide in the exhaust. This may make the use of an oxidation catalyst more problematic, as both reactants are present in small amounts. However, the large amount of water vapor in the exhaust can maintain a high rate of conversion of the CO in the water gas shift reaction.

FIG. 1 is a schematic diagram of a gas turbine system 100 that includes a gas turbine engine 102. The gas turbine engine 102 may have a compressor 104 and a turbine expander 106 on a single shaft 108. The gas turbine engine 102 is not limited to a single shaft arrangement, as multiple shafts could be used, generally with mechanical linkages or transmissions between shafts. In various embodiments, the gas turbine engine 102 also has a number of combustors 110 that feed hot exhaust gas to the expander, for example, through lines 112. For example, a gas turbine 102 may have 2, 4, 6, 14, 18, or even more combustors 110, depending on the size of the gas turbine 102.

The combustors 110 are used to burn a fuel provided by a fuel source 114. An oxidant may be provided to each of the combustors 110 from various sources. For example, in embodiments, an external oxidant source 116, such as an external compressor, may provide the oxidant to the combustors 110. In embodiments, an oxidant or recycled exhaust gases 118, or a mixture thereof, may be compressed in the compressor 104 and then provided to the combustors 110. In other embodiments, such as when an external oxidant source 116 is provided, the compressor 104 may be used to compress only the recycled exhaust gas, which may be fed to the combustors 110 for cooling and dilution of the oxidant.

The exhaust gas from the combustors 110 expands in the turbine expander 106, creating mechanical energy. The mechanical energy may power the compressor 104 through the shaft 108. Further, a portion of the mechanical energy may be harvested from the gas turbine as a mechanical power output 120, for example, to generate electricity or to power oxidant compressors. The expanded exhaust gas 122 may be vented, used for heat recovery, recycled to the compressor 104, or used in any combinations thereof. In an embodiment, the exhaust gas 122 is flowed through one or more catalyst beds that include a water gas shift catalyst, and oxidation catalyst, or both.

In some embodiments, the oxidant is metered to the combustors 110 to control an equivalence ratio of the fuel to the oxidant. The metering may be performed for all combustors 110 together, for example, by adjusting the fuel 114 and oxidant 116 sources, or each individual combustor 110. It will be apparent to one of skill in the art that a stoichiometric burn, e.g., at an equivalence ratio of 1, will be hotter than a non-stoichiometric burn. Therefore, either excess oxidant or an added non-combustible gas, such as a recycle exhaust gas, can be added to cool the engine, preventing damage to the combustors 110 or the turbine expander 106 from the extreme heat.

The use of recycled exhaust gas 122 provides a further advantage in that the exhaust is deficient in oxygen, making it a better material for enhanced oil recovery. Adjusting individual combustors 110 may compensate for differences between the combustors 110, improving the overall efficiency of the gas turbine 102.

Control of Combustors

FIG. 2 is a schematic of a gas turbine system 200 that can be used to adjust the oxidant flow and/or fuel flow to the combustors 110 of a gas turbine engine 102. The referenced units are as generally discussed with respect to FIG. 1. The system 200 may adjust the amount of oxidant 116 provided to the combustors 110, for example, by adjusting the pressure, flow rate, or composition of the oxidant 116. Similarly, the system 200 may adjust the amount of fuel 114 provided to the combustors 110 by adjusting the pressure, flow rate, or composition of the fuel 114. In an embodiment, the oxidant flow to each individual combustor 110 may be adjusted by an oxidant flow adjusting device 202, such as a valve, swirler, or mixing section in each combustor 110. An actuator 204 can be used to adjust the oxidant flow adjusting device 202. Similarly, the fuel flow 114 to each individual combustor 110 may be adjusted.

A number of sensors 206 can be placed in an expander exhaust section 208 of the gas turbine engine 102, for example, 5, 10, 15, 20, 25, 30 or more, sensors 206 may be placed in a ring around the expander exhaust section 208. The number of sensors 206 may be determined by the size of the gas turbine 102, the number of combustors 110, or both. The sensors 206 may include oxygen sensors, carbon monoxide sensors, temperature sensors, hydrogen sensors, and the like. Examples of oxygen sensors can include lambda and/or wideband zirconia-oxygen sensors, titania sensors, galvanic, infrared, or any combination thereof. Examples of temperature sensors can include thermocouples, resistive temperature devices, infrared sensors, or any combination thereof. Examples of carbon monoxide sensors can include oxide based film sensors such as barium stannate and/or titanium dioxide. For example, a carbon monoxide sensor can include platinum-activated titanium dioxide, lanthanum stabilized titanium dioxide, and the like. The choice of the sensors 206 may be controlled by the response time, as the measurements are needed for real time control of the system. The sensors 206 may also include combinations of different types of sensors 206. The sensors 206 send a signal 210 back to the control system 212, which may be used to make fuel and oxidant adjustment decisions for each, or all, of the combustors 110. Any number of physical measurements could be performed, for example, the sensors 206 could be used to measure temperature, pressure, CO concentration, 0 2 concentration, vibration, and the like. Further, multiple sensors 206 could be used to measure combinations of these parameters.

The control system 212 may be part of a larger system, such as a distributed control system (DCS), a programmable logic controller (PLC), a direct digital controller (DDC), or any other appropriate control system. Further, the control system 212 may automatically adjust parameters, or may provide information about the gas turbine 102 to an operator who manually performs adjustments. The control system 212 is discussed further with respect to FIG. 7, below.

It will be understood that the gas turbine system 200 shown in FIG. 2, and similar gas turbine systems depicted in other figures, have been simplified to assist in explaining various embodiments of the present techniques. Accordingly, in embodiments of the present techniques, both the oxidant system 116 and the fuel system 114, as well as the gas turbine systems themselves, can include numerous devices not shown. Such devices can include flow meters, such as orifice flow meters, mass flow meters, ultrasonic flow meters, venturi flow meters, and the like. Other devices can include valves, such as piston motor valves (PMVs) to open and close lines, and motor valves, such as diaphragm motor valves (DMVs), globe valves, and the like, to regulate flow rates. Further, compressors, tanks, heat exchangers, and sensors may be utilized in embodiments in addition to the units shown.

In the embodiment shown in FIG. 2, the compressor 104 may be used to compress a stream 214, such as a recycled exhaust stream. After compression, the stream 214 may be injected from a line 216 into the mixing section of the combustor 110. The stream 214 is not limited to a pure recycle stream, as the injected stream 216 may provide the oxidant to the combustor 110. The exhaust stream 218 from the expander exhaust section 208 may be used to provide the recycle stream, as discussed further with respect to FIG. 2, below.

Catalyst and Adsorbent Beds

The exhaust stream 218 may be passed through one or more catalyst beds 308, for example, attached to the exhaust expander section 208, located in an HRSG, located near an HSRG, or in other places in the gas turbine system 200. Multiple catalyst beds may be used in sequence. Generally, an oxidation and/or reduction catalyst bed may be located in a high temperature zone and draw its heat from, for example, an exhaust expander section 208 or a heat recovery steam generator (HRSG), as discussed herein. Preferably, the temperature of the catalyst beds reaches 375° C. or a sufficient temperature to enable the catalyzed reaction to occur.

As illustrated in FIG. 2, when the exhaust stream 218 exits the HRSG, it is passed to one or more catalyst beds 308. The exhaust stream 218 may contain CO, CO2, N2, and/or methane. When passed to the catalyst beds, CO in the exhaust stream 218 is consumed by a reaction catalyzed by the catalyst beds and producing CO₂. The materials of the catalyst beds 308 may double as adsorbents, adsorbing the newly formed CO₂. When the catalyst beds 308 have adsorbed some amount of CO₂, the catalyst beds 308 are then purged to with a regenerant stream 309 to release the CO₂. The combined product of the regenerant stream and adsorbed CO₂ is released from the catalyst beds 308 in recovery stream 311.

Adsorption of CO₂ at the catalyst beds preferably occurs at the pressure of the exhaust stream when it reaches the catalyst beds 308. In order to purge the adsorbed CO₂ from the catalyst beds 308, the pressure at the catalyst beds 308 is reduced by a blow down process. Once the pressure is adequately reduced at the catalyst beds 308 to release the adsorbed CO₂, the regenerant stream 309 can be directed to the catalyst beds 308 for effective purging.

The catalyst beds 308 operate at a high temperature and draw their heat from, for example, the HSRG. A primary advantage of this is that when purging the catalyst beds 308 with regenerant stream 309, the regenerant stream may comprise N₂ or steam, but it also may comprise liquid water. Because of the temperature at which the beds are operated, when liquid water is introduced to the catalyst beds 308, some heat from the catalyst beds 308 is transferred to the liquid water to form steam. Therefore, energy need not be extracted from another point on the power generation cycle to extract steam for the purge, which is a particularly economically taxing aspect of emissions capture.

When the regenerant stream 309 is passed to the catalyst beds 308, the adsorbed CO₂ on the catalyst beds 308 mixes with the regenerant stream 309 and is released in recovery stream 311. Regenerant stream 309 is passed to the catalyst beds 308 for a sufficient time period or in a sufficient time period to substantially release the adsorbed CO₂ from the beds. The resulting recovery stream 311 is a mixture of at least CO₂ and steam. Once recovery stream 311 has left the catalyst beds 308, the recovery stream 311 may be cooled and condensed to isolate the CO₂ from the steam and recover energy from the steam.

Multiple beds can be used in the catalyst beds 308 where typically every bed sequentially goes through the same cycle. When a first bed satisfies a condition, the feed flow can be switched to a second bed. These conditions may be any of the following: a predetermined period of feed time has passed, the feed flow can be stopped based on a predetermined schedule, based on detection of breakthrough of one or more heavy components, based on adsorption of the heavy component(s) corresponding to at least a threshold percentage of the total capacity of the adsorbent, or based on any other convenient criteria. The first bed can then be regenerated by having the adsorbed gases released via a purge. To allow for a continuous feed flow, a sufficient number of or catalyst beds are preferably used so that the first bed is finished regenerating prior to at least one other bed satisfying the condition for switching beds.

In an alternative embodiment, as illustrated in FIG. 3, there may be included additional non-catalyst beds to which the exhaust stream is directed. As discussed above with respect to FIG. 2, a portion of the exhaust stream 218 may be directed to catalyst beds 308. A second portion of the exhaust stream 218 and/or a portion of the recovery stream 311 may additionally be directed to non-catalyst beds for adsorption of CO₂. When catalyst beds 308 react CO to form CO₂ and that CO₂ is subsequently adsorbed and purged, the recovery stream 311 is concentrated with CO₂. By passing recovery stream 311 to non-catalyst adsorbent beds, the CO₂ content in the recovery stream 311 can further be isolated and further concentrated. The non-catalyst beds preferably undergo the same cycling processes as discussed above with relation to the catalyst beds 308.

The sensors 206 are not limited to the expander exhaust section 208, but may be in any number of other locations, instead of or in addition to the expander exhaust section 208. For example, the sensors 206 may be disposed in multiple rings around the expander exhaust section 208. Further, the sensors 206 may be separated into multiple rings by the type of sensor 206, for example, with oxygen analyzers in one ring and temperature sensors in another ring. Sensors 224 may also be located in the product gas stream 222 from the catalyst beds 308.

The recovered carbon dioxide may be injected into a subterranean reservoir for enhanced hydrocarbon recovery. Carbon dioxide may also be injected into a sequestration well or may be provided as a gaseous product to market. The carbon dioxide stream may also be processed in a dehydration unit to lower the dewpoint prior to sales. The carbon dioxide stream may further be passed through an expander to recovery mechanical energy prior to venting the stream.

While embodiments in this section have been discussed in relation to a gas turbine system, it is also contemplated that the above configurations are applicable to a hydrogen generation system or other comparable system. For example, a fuel reforming reactor may be substituted for the combustor above and the inputs thereto may be methane and steam, which act as a fuel and oxidant, respectively. When methane and steam are combusted in the fuel reforming reactor, H₂ and CO₂ are produced as products in the exhaust gas. The exhaust gas created as a result of the hydrogen generation process may then be passed to the catalyst beds 308, where the CO₂ is adsorbed as discussed above. In addition to sequestering CO₂ in the adsorbent bed, a stream of concentrated H₂ may be produced as H₂ is not adsorbed by the exemplary catalyst materials discussed herein. This concentrated H₂ may then be captured and used in numerous applications.

Catalyst Materials

Preferably, the materials used in the catalyst beds 308 enable a reaction which consumes CO in the exhaust gas and produces CO₂. The catalyst beds also preferably have suitable adsorption properties to adsorb the CO₂ once it is produced.

One example of a material suitable for the catalyst beds includes a mixed metal oxide adsorbent, such as an adsorbent including a mixture of an alkali metal carbonate and an alkaline earth metal oxide and/or a transition metal oxide. Examples of suitable alkali metal carbonates can include, but are not limited to, a carbonate of lithium, sodium, potassium, rubidium, cesium, or a combination thereof, e.g., a carbonate of lithium, sodium, potassium, or a combination thereof. Examples of suitable alkaline earth metal oxides can include, but are not limited to, oxides of magnesium, calcium, strontium, barium, or a combination thereof, e.g., oxides of magnesium and/or calcium. Some examples of suitable transition metal oxides can include, but are not limited to, oxides of lanthanide series metals, such as lanthanum, and/or of transition metals that can form oxides with the metal in a +2 or +3 oxidation state (such as yttrium, iron, zinc, nickel, vanadium, zirconium, cobalt, or a combination thereof).

In some aspects, the carbonate can be selected independently from the oxide in the mixed metal oxide. In such aspects, the carbonate can include, consist essentially of, or be lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, and/or cesium carbonate (e.g., lithium carbonate, sodium carbonate, and/or potassium carbonate; lithium carbonate and/or potassium carbonate; lithium carbonate and/or sodium carbonate; or sodium carbonate and/or potassium carbonate).

In aspects where the carbonate is selected independently from the oxide, the oxide can be an alkaline earth oxide, a transition metal oxide, a combination of two or more alkaline earth oxides, a combination of two or more transition metal oxides, or a combination of oxides including at least one alkaline earth oxide and at least one transition metal oxide. In aspects where the independently selected oxide includes one or more alkaline earth oxides, a suitable alkaline earth oxide can include, consist essentially of, or be magnesium oxide, calcium oxide, strontium oxide, and/or barium oxide, e.g., including at least magnesium oxide and/or calcium oxide.

In aspects where the independently selected oxide includes one or more transition metal oxides, suitable transition metals can include, consist essentially of, or be one or more transition metals that can form oxides with the metal in a +2 or +3 oxidation state (e.g., yttrium oxide, iron oxide, zinc oxide, nickel oxide, vanadium oxide, cobalt oxide, zirconium oxide, lanthanum oxide, other oxides of lanthanide metals, and/or a combination thereof). One preferred option includes a transition metal oxide selected from lanthanum oxide and/or zirconium oxide. Another option includes a metal oxide selected from lanthanum oxide, yttrium oxide, zirconium oxide, and/or zinc oxide. Yet another option includes a metal oxide selected from nickel oxide, cobalt oxide, and/or iron oxide. Mixtures within each of these options and/or across options are also contemplated, such as mixtures of lanthanum oxide with zinc oxide and/or vanadium oxide; mixtures of lanthanum oxide with iron oxide, cobalt oxide, and/or nickel oxide; mixtures of zirconium oxide with yttrium oxide, zinc oxide, and/or vanadium oxide; and mixtures of zirconium oxide with iron oxide, cobalt oxide, and/or nickel oxide.

In aspects where the independently selected oxide includes one or more alkali metal oxides and one or more transition metal oxides, suitable alkali metal oxides can include, consist essentially of, or be magnesium oxide, calcium oxide, strontium oxide, and/or barium oxide, while suitable transition metals can include, consist essentially of, or be transition metals that can form oxides with the metal in a +2 or +3 oxidation state, such as yttrium oxide, iron oxide, zinc oxide, nickel oxide, vanadium oxide, cobalt oxide, zirconium oxide, lanthanum oxide, and/or other lanthanide oxides. Each of these alkali metal oxides and transition metal oxides can be independently selected individually or in any combination of multiple transition metal oxides. Examples of mixtures can include, consist essentially of, or be a mixture of oxides where at least one oxide is lanthanum oxide, zirconium oxide, and/or magnesium oxide; a mixture of oxides where the mixture includes at least two of lanthanum oxide, zirconium oxide, and magnesium oxide; a mixture of oxides where one oxide is magnesium oxide and/or calcium oxide; and/or a mixture of oxides where at least one oxide is lanthanum oxide, yttrium oxide, and/or zirconium oxide.

In some alternative aspects, a mixed metal oxide can include an alkaline earth carbonate in combination with a transition metal oxide. In such aspects, the alkaline earth carbonate can include, consist essentially of, or be magnesium carbonate and/or calcium carbonate. Additionally or alternately, the alkaline earth carbonate can be present in a mixture with an alkali metal carbonate. Examples of such carbonate mixtures can include, consist essentially of, or be mixtures of lithium carbonate with magnesium carbonate, lithium carbonate with calcium carbonate, potassium carbonate with magnesium carbonate, potassium carbonate with calcium carbonate, sodium carbonate with magnesium carbonate, and sodium carbonate with calcium carbonate (e.g., lithium carbonate with magnesium carbonate or potassium carbonate with magnesium carbonate). In such aspects, suitable transition metals can include, consist essentially of, or be transition metals that can form oxides with the metal in a +2 or +3 oxidation state, such as yttrium oxide, iron oxide, zinc oxide, nickel oxide, vanadium oxide, cobalt oxide, zirconium oxide, lanthanum oxide, other lanthanide oxides, and/or a combination thereof. Each of these alkaline earth carbonates and transition metal oxides can be independently selected individually or in any combination of multiple alkaline earth carbonates and/or multiple transition metal oxides. For the transition metal oxide, one preferred option can include a transition metal oxide selected from lanthanum oxide or zirconium oxide. Another option can include a metal oxide selected from lanthanum oxide, yttrium oxide, zirconium oxide, and/or zinc oxide. Yet another option can include a metal oxide selected from nickel oxide, cobalt oxide, and/or iron oxide. Mixtures within each of these options and/or across options are also contemplated, such as mixtures of oxides where at least one oxide is lanthanum oxide and/or zirconium oxide; mixtures of lanthanum oxide with zinc oxide and/or vanadium oxide; mixtures of lanthanum oxide with iron oxide, cobalt oxide, and/or nickel oxide; mixtures of zirconium oxide with yttrium oxide, zinc oxide, and/or vanadium oxide; and/or mixtures of zirconium oxide with iron oxide, cobalt oxide, and/or nickel oxide.

Additional or alternative materials can include hydrotalcites.

Energy Recovery and Recycle of Exhaust

FIG. 3 is a schematic of a gas turbine system that includes an HRSG 302 on the exhaust stream 218 from the expander exhaust section 208. The HRSG 302 may include any number of heat recovery units, such as a steam superheating device, a steam raising device, a feed water heating device, or an endothermic reaction device, among others. Thus, any HRSG 302 referred to herein may be replaced with any other type of heat recovery unit. The exhaust gas in the exhaust stream 218 can include, but is not limited to, unburned fuel, oxygen, carbon monoxide, carbon dioxide, hydrogen, nitrogen, nitrogen oxides, argon, water, steam, or any combinations thereof. The exhaust stream 218 can have a temperature ranging from about 430° C. to about 725° C. and a pressure of about 101 kPa to about 110 kPa.

In the embodiment shown in the schematic, the heat generated by the combustion can be used to boil an inlet water stream 304 to generate a steam stream 306 that may also be superheated. The steam stream 306 may be used, for example, in a Rankine cycle to generate mechanical power from a steam turbine, or to provide steam for utilities, or both. The mechanical power from the steam turbine may be used to generate electricity, operate compressors, and the like. As noted herein, the gas turbine system 300 is not limited to a HRSG 302, as any type of heat recovery unit (HRU) may be used. For example, the heat may be recovered in a heat exchanger to provide hot water or other heated fluids. Further, a Rankine cycle based on an organic working fluid (ORC) may be used to recover heat energy by converting it to mechanical energy.

In an embodiment, one or more catalyst beds 308 may be located in the HRSG 302 and described herein. The catalyst beds 308 may be located within the HRSG 302 by the reaction temperature desired for the catalyst. For example, a catalyst that operates at a higher temperature, such as an oxidation catalyst, may be located in the HRSG 302 at a point just after the exhaust stream 218 enters the HRSG 302. Similarly, a catalyst that operates at a lower temperature may be located at a later point in the HRSG 302, for example, just before a product gas 310 leaves the HRSG 302.

The cooled exhaust stream or product gas 310 may then be used for other purposes, such as to provide recycle gas for stream 214. Various other sensors may be added to the system to monitor and control the catalytic reaction. For example, sensors 312 may be placed in the product gas 310 to determine the efficacy of the catalytic reactions. These sensors 312 may be used in addition to the sensors 206 on the expander exhaust section 208 to determine the reactants present, and to control the fuel and oxidant levels.

Individual Control of Equivalence Ratio to Combustors

The gas turbine systems discussed above may be used to control the combustion process in the combustors 110, either individually, as a group, or both. A goal of the control may be to balance the equivalence ratio of the fuel and oxygen. This may be performed to minimize unburned or partially burned hydrocarbon, represented by the CO concentration in an exhaust stream and to minimize unconsumed oxygen in the exhaust stream. The equivalence ratio is discussed further with respect to FIG. 4A.

FIGS. 4A and 4B are graphical depictions of a simulation showing the equilibrium relationship between the mole fraction 402 of oxygen and carbon monoxide as the equivalence ratio (φ) 404 changes from 0.75 to 1.25 and from 0.999 to 1.001, respectively. The highest efficiency may be achieved when the equivalence ratio is about 1.0. The oxygen concentration as a function of the equivalence ratio is shown as line 406 and the carbon monoxide concentration as a function of the equivalence ration is shown as line 408. The equivalence ratio (φ) 404 is equal to (mol % fuel/mol % oxygen)_(actual)/(mol % fuel/mol % oxygen)_(stoichiometric). The mol % fuel is equal to F_(fuel)/(F_(oxygen)+F_(fuel)), where F_(fuel) is equal to the molar flow rate of fuel and F_(oxygen) is equal to the molar flow rate of oxygen.

The mol % oxygen is equal to F_(oxygen)/(F_(oxygen)+F_(fuel)), where F_(oxygen) is equal to the molar flow rate of oxygen and F_(fuel) is equal to the molar flow rate of fuel. The molar flow rate of the oxygen depends on the proportion of oxygen to diluent in the oxidant mixture, and may be calculated as F_(oxygen)/(F_(oxygen)+F_(diluent)). As used herein, the flow rate of the oxidant may be calculated as F_(oxidant)=(F_(oxygen)+F_(diluent)).

As the equivalence ratio (φ) 404 goes below 1 or above 1 the mole fraction or concentration of oxygen and carbon dioxide in the exhaust gas changes. For example, as the equivalence ratio (φ) 404 goes below 1 the mole fraction of oxygen rapidly increases from about 1 ppm (i.e., an oxygen mole fraction of about 1.0×10⁻⁶) at an equivalence ratio (φ) 404 of about 1 to about 100 ppm (i.e., an oxygen mole fraction of about 1×10−4) at an equivalence ratio (φ) 404 of about 0.999. Similarly, as the equivalence ratio (φ) 404 goes above 1 the concentration of carbon monoxide rapidly increase from about 1 ppm (i.e., carbon monoxide mole fraction of about 1×10⁻⁶) at an equivalence ratio (φ) 404 of about 0. 9995 to greater than about 100 ppm (i.e., a carbon monoxide mole fraction of about 1×10⁻⁴) at an equivalence ratio (φ) 404 of about 1.001.

Based, at least in part, on the data obtained from the sensors, such as sensors 206, or 312, the amount of oxidant 116 and/or the amount of fuel 114 the combustors 110 can be adjusted to produce an exhaust stream 218 having a desired composition. For example, monitoring the oxygen and/or carbon monoxide concentration in the exhaust gas in the expander exhaust section 208 or the cooled exhaust stream 310 allows the adjustment of the amount of oxidant 116 and fuel 114 introduced the combustors 110, either individual or as an ensemble, to be controlled such that combustion of the fuel 114 is carried out within a predetermined range of equivalence ratios (φ) 404 in the gas turbine engine 102. This can be used to produce an exhaust stream 218 having a combined concentration of oxygen and carbon monoxide of less than about 3 mol %, less than about 2.5 mol %, less than about 2 mol %, less than about 1.5 mol %, less than about 1 mol %, or less than about 0.5 mol %. Furthermore, the exhaust stream 218 may have less than about 4,000 ppm, less than about 2,000 ppm, less than about 1,000 ppm, less than about 500 ppm, less than about 250 ppm, or less than about 100 ppm combined oxygen and carbon monoxide. In some embodiments, the fuel 114 and oxidant 116 are adjusted to form a slightly rich mixture to enhance the formation of CO at the expense of the 0 2, favoring the water gas shift reaction. In other embodiments, a slightly lean mixture is formed, to enhance the formation of O₂ at the expense of CO and unburned hydrocarbons, favoring an oxidation reaction.

However, as the exhaust will contain a much higher content of water vapor, for example, at about 10,000 ppm or higher, than any other reactive component, the water gas shift reaction may more favorable.

A desired or predetermined range for the equivalence ratio (φ) 404 in the combustors 110 can be calculated or entered to carry out the combustion of the fuel 114 to produce a mixed exhaust stream 418 containing a desired amount of oxygen and/or carbon monoxide. For example, the equivalence ratio (φ) in the combustors 110 can be maintained within a predetermined range of from about 0.85 to about 1.15 to produce an exhaust stream 218 having a combined oxygen and carbon monoxide concentration ranging from a low of about 0.5 mol %, about 0.8 mol %, or about 1 mol %, to a high of about 1.5 mol %, about 1.8 mol %, about 2 mol %, or about 2.2 mol %. In another example, the equivalence ratio (φ) 404 in the combustors 110 can be maintained within a range of about 0.85 to about 1.15 to produce an exhaust stream 218 having a combined oxygen and carbon monoxide concentration of less than 2 mol %, less than about 1.9 mol %, less than about 1.7 mol %, less than about 1.4 mol %, less than about 1.2 mol %, or less than about 1 mol %. In still another example, the equivalence ratio (φ) 404 in the combustors 110 can be maintained within a range of from about 0.96 to about 1.04 to produce an exhaust stream 218 having a combined oxygen and carbon monoxide concentration of less than about 4,000 ppm, less than about 3,000 ppm, less than about 2,000 ppm, less than about 1,000 ppm, less than about 500 ppm, less than about 250 ppm, or less than about 100 ppm.

It will be noted that in embodiments in which the combustors 110 are individually controlled, the combustors 110 do not have to be at the same set-point, or even within the same range. In various embodiment, different or biased set-points may be used for each of the combustors 110 to account for differences in construction, performance, or operation. This may avoid a situation in which different operational characteristics of different combustors 110 cause the exhaust stream 218 to be contaminated with unacceptable levels of oxygen or carbon monoxide. Also, it will be noted that a combination of combustion efficiency less that 100% and equivalence ratio differences among the individual combustors 110 may result in both CO 408 and oxygen 406 levels greater than those shown in FIGS. 4A and 4B at a given global equivalence ratio 404.

Accordingly, in embodiments of the present techniques, two methods for operating the gas turbine 102 are used. In a first method, the entire set of combustors 110 is operated as a single entity, for example, during startup and in response to global set-point adjustments, such as speed or power changes. In a second method, the individual combustors 110 may be separately biased, for example, to compensate for differences in wear, manufacturing, and the like.

One method for operating the entire set of combustors 110 can include initially, i.e., on start-up, introducing the fuel 114 and oxygen in the oxidant 116 at an equivalence ratio (φ) 404 greater than 1. For example, the equivalence ratio (φ) 404 at startup may range from a low of about 1.0001, about 1.0005, about 1.001, about 1.05, or about 1.1, to a high of about 1.1, about 1.2, about 1.3, about 1.4, or about 1.5. In another example, the equivalence ratio (φ) 404 can range from about 1.0001 to about 1.1, from about 1.0005 to about 1.01, from about 1.0007 to about 1.005, or from about 1.01 to about 1.1. For global adjustments, the concentration of oxygen and/or carbon monoxide in the exhaust stream 218 can be determined or estimated via the sensors 206, 224, or 312. The expanded exhaust gas in the exhaust stream 218 may initially have a high concentration of carbon monoxide (e.g., greater than about 1,000 ppm or greater than about 10,000 ppm) and a low concentration of oxygen (e.g., less than about 10 ppm or less than about 1 ppm).

Another method for operating the entire set of combustors 110 can include initially, i.e., on start-up, introducing the fuel 114 and oxygen in the oxidant 116 at an equivalence ratio (φ) 404 of less than 1. For example, the equivalence ratio (φ) 404 at startup may range from a low of about 0.5, about 0.6, about 0.7, about 0.8, or about 0.9 to a high of about 0.95, about 0.98, about 0.99, about 0.999. In another example, the equivalence ratio (φ) 404 can range from about 0.9 to about 0.999 from about 0.95 to about 0.99, from about 0.96 to about 0.99, or from about 0.97 to about 0.99. The expanded exhaust gas in the exhaust stream 218 may initially have a high concentration of oxygen (e.g., greater than about 1,000 ppm or greater than about 10,000 ppm) and a low concentration of carbon monoxide (e.g., less than about 10 ppm or even less than about 1 ppm).

For example, when the concentration of oxygen in the exhaust gas increases from less than about 1 ppm to greater than about 100 ppm, about 1,000 ppm, about 1 mol %, about 2 mol %, about 3 mol %, or about 4 mol %, an operator, the control system 212, or both can be alerted that an equivalence ratio (φ) 404 of less than 1 has been reached. In one or more embodiments, the amount of oxygen via oxidant 116 and fuel 114 can be maintained constant or substantially constant to provide a combustion process having an equivalence ratio (φ) 404 of slightly less than 1, e.g., about 0.99. The amount of oxygen via oxidant 116 can be decreased and/or the amount of fuel 114 can be increased and then maintained at a constant or substantially constant amount to provide a combustion process having an equivalence ratio (φ) 404 falling within a predetermined range. For example, when the concentration of oxygen in the exhaust stream 418 increases from less than about 1 ppm to about 1,000 ppm, about 0.5 mol %, about 2 mol %, or about 4 mol %, the amount of oxygen introduced via the oxidant 116 can be reduced by an amount ranging from a low of about 0.01%, about 0.02%, about 0.03%, or about 0.04% to a high of about 1%, about 2%, about 3%, or about 5% relative to the amount of oxygen introduced via the oxidant 116 at the time the increase in oxygen in the exhaust gas is initially detected. In another example, when the concentration of oxygen in the exhaust stream 218 increases from less than about 1 ppm to about 1,000 ppm or more the amount of oxygen introduced via the oxidant 116 can be reduced by about 0.01% to about 2%, about 0.03% to about 1%, or about 0.05% to about 0.5% relative to the amount of oxygen introduced via the oxidant 116 at the time the increase in oxygen in the exhaust gas is detected. In still another example, when the concentration of oxygen increases from less than about 1 ppm to about 1,000 ppm or more the amount offue1114 can be increased by an amount ranging from a low of about 0.01%, about 0.02%, about 0.03%, or about 0.04% to a high of about 1%, about 2%, about 3%, or about 5% relative to the amount of fuel 114 introduced at the time the increase in oxygen in the exhaust gas is initially detected.

During operation of the gas turbine system 102, the equivalence ratio (φ) 404 can be monitored via the sensors 206, 224, or 312 on a continuous basis, at periodic time intervals, at random or non-periodic time intervals, when one or more changes to the gas turbine system 102 occur that could alter or change the equivalence ratio (φ) 404 of the exhaust stream 218, or any combination thereof. For example, changes that could occur to the gas turbine system 102 that could alter or change the equivalence ratio (φ) 404 can include a change in the composition of the fuel, a change in the composition of the oxidant, a degradation of the catalyst, for example, due to carbon formation, or a combination thereof. As such, the concentration of oxygen and/or carbon monoxide, for example, can be monitored, and adjustments can be made to the amount of oxidant 116 and/or fuel 114 to control the amounts of oxygen and/or carbon monoxide in the exhaust stream 218, the product gas 310, or both. In at least one embodiment, reducing the equivalence ratio (φ) 404 can be carried out in incremental steps, non-incremental steps, a continuous manner, or any combination thereof. For example, the amount of oxidant 116 and/or the fuel 114 can be adjusted such that the equivalence ratio (φ) 404 changes by a fixed or substantially fixed amount per adjustment to the oxidant 116 and/or fuel 114, e.g., by about 0.001, by about 0.01, or by about 0.05. In another example, the amount of oxidant 116 and/or fuel 114 can be continuously altered such that the equivalence ratio (φ) 404 continuously changes. Preferably the amount of oxidant 116 and/or fuel 114 is altered and combustion is carried out for a period of time sufficient to produce an exhaust gas of substantially consistent composition, at which time the amount of oxidant 116 and/or fuel 114 can be adjusted to change the equivalence ratio (φ) 404 in an amount ranging from a low of about 0.00001, about 0.0001, or about 0.0005 to a high of about 0.001, about 0.01, or about 0.05. After the exhaust stream 218 achieves a substantially consistent concentration of oxygen the oxidant 116 and/or fuel 114 can again be adjusted such that the equivalence ratio (φ) 404 changes. The amount of oxygen and/or carbon monoxide in the exhaust stream 418 can be monitored and the amount of oxidant 116 and/or fue1 114 can be repeatedly adjusted until the exhaust stream 218 has a combined concentration of oxygen and carbon monoxide, for example, of less than about 2 mol % or less than about 1.5 mol %, or less than about 1 mol %.

The combustors 110 can be operated on a continuous basis such that the exhaust stream 218 has a combined oxygen and carbon monoxide concentration of less than 2 mol %, less than 1 mol %, less than 0.5 mol %, or less than about 0.1 mol %. In another example, the time during which combustion is carried out within the combustors 110, the exhaust stream 418 can have a combined oxygen and carbon monoxide concentration of less than 2 mol % or less than about 1 mol % for about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or about 95% of the time during which the gas turbine engine102 is operated. In other words, for a majority of the time that combustion is carried out within the combustors 110, the exhaust stream 418 can have a combined oxygen and carbon monoxide concentration of less than about 2 mol %, less than about 1 mol %, less than about 0.5 mol %, or less than about 0.1 mol %.

Once the overall control of the gas turbine engine 102 is set, the biasing needed for individual combustors 110 may be determined. For example, an oxidant flow adjusting device 202 for each individual combustor 110 can be adjusted by the control system 212 to maintain the measured value of the sensors 206, 224, or 312 at or near to a desired set-point. Several calculated values may be determined from the measured values of each sensor 206 or 312. These may include, for example, an average value that can be used to make similar adjustments to all of the oxidant flow adjusting devices 202 in then combustors 110.

In addition, various difference values, for example, calculated based on differences of the measured values of two or more sensors 206, 224, or 312, may be used to make biasing adjustments to the oxidant flow adjusting devices 202 on one or more of the combustors 110 to minimize differences between the measured values of the sensors 206, 224, or 312. The control system 212 may also adjust the oxidant system 116 directly, such by adjusting compressor inlet guide vanes (IGV) or a speed control to change the oxidant flow rates, for example, to all of the combustors 110 at once. Further, the control system 212 can make similar adjustments to the fue1 114 to all combustors 110, depending, for example, on the speed selected for the gas turbine 102. As for the oxidant, the fuel supply to each of the combustors 110 may be individually biased to control the equivalence ratio of the bum. This is discussed further with respect to FIG. 6.

FIG. 5 is a block diagram of a method 500 for adjusting fuel and oxidant levels to the combustors 110 based on readings from an array of sensors 206, 224, and 312. Like numbered items are as described in FIGS. 1, 2, and 3. It can be assumed that the gas turbine engine 102 has been started before the method 500 begins, and that all of the combustors 110 are using essentially the same mixture or a previous operation point. The method 500 begins at block 502, when a set-point for the oxidant 116 is entered and oxidant is provided to the combustors 110. In a substantially simultaneous manner, at block 504, a set-point is entered for the fuel 114, and fuel 114 is provided to the combustors 110. At block 506, the combustion process consumes the fue1 114 and oxidant 116 provided.

At block 508, the exhaust gas is passed through one or more catalyst beds, for example, including oxidation catalysts, water gas shift catalysts, or both. At block 510, readings are obtained from the sensors 206, 224, or 312. The readings may indicate the efficacy of the catalyst processes, by determining the concentrations of H₂O, O₂, CO₂, H₂, and other gas components. These may be used to determine global adjustments to the combustors. Further, individual sensors 206 along the exhaust expander ring 208 may be used to determine sums and differences of concentrations from individual combustors 110. The sums and differences may be combined to assist in identifying the combustors 110 that are contributing to a high oxygen or high carbon monoxide condition in the exhaust. This may also be performed by a swirl chart, as described above. Adjustments to the fuel 114 and oxidant 116 for those combustors 110 may be calculated and added to any global adjustments. Process flow then returns to blocks 502 and 504 with the new set points, wherein the method 500 repeats.

Control System

FIG. 6 is a block diagram of a plant control system 600 that may be used to control the oxidant 116 and fuel 114 to the combustors 110 in a gas turbine engine 102. As previously mentioned, the control system 600 may be a DCS, a PLC, a DDC, or any other appropriate control device. Further, any controllers, controlled devices, or monitored systems, including sensors, valves, actuators, and other controls, may be part of a real-time distributed control network, such as a FIELDBUS system, in accordance with IEC 61158. The plant control system 600 may host the control system 212 used to adjust the fue1 114 and oxidant 116 to the combustors 110, individually or as an ensemble.

The control system 600 may have a processor 602, which may be a single core processor, a multiple core processor, or a series of individual processors located in systems through the plant control system 600. The processor 602 can communicate with other systems, including distributed processors, in the plant control system 600 over a bus 604. The bus 604 may be an Ethernet bus, a FIELD BUS, or any number of other buses, including a proprietary bus from a control system vendor. A storage system 606 may be coupled to the bus 604, and may include any combination of non-transitory computer readable media, such as hard drives, optical drives, random access memory (RAM) drives, and memory, including RAM and read only memory (ROM). The storage system 606 may store code used to provide operating systems 608 for the plant, as well as code to implement turbine control systems 610, for example, bases on the first or second methods discussed above.

A human-machine interface 612 may provide operator access to the plant control system 600, for example, through displays 614, keyboards 616, and pointing devices 618 located at one or more control stations. A network interface 620 may provide access to a network 622, such as a local area network or wide area network for a corporation.

A plant interface 624 may provide measurement and control systems for a first gas turbine system. For example, the plant interface 624 may read a number of sensors 626, such as the sensors 206, 224, and 312 described with respect to FIGS. 2 and 3. The plant interface 624 may also make adjustments to a number of controls, including, for example, fuel flow controls 628 used adjust the fuel 114 to the combustors 110 on the gas turbine 102. Other controls include the oxidant flow controls 630, used, for example, to adjust the actuator 404 on an oxidant flow adjusting device 402, the actuator 706 on a oxidant flow adjusting valve 702, or both, for each of the combustors 110 on the gas turbine 102. The plant interface 624 may also control other plant systems 632, such as generators used to produce power from the mechanical energy provided by the gas turbine 102. The additional plant systems 632 may also include the compressor systems used to provide oxidant 116 to the gas turbine 102.

The plant control system 600 is not limited to a single plant interface 624. If more turbines are added, additional plant interfaces 634 may be added to control those turbines. Further, the distribution of functionality is not limited to that shown in FIG. 6. Different arrangements could be used, for example, one plant interface system could operate several turbines, while another plant interface system could operate compressor systems, and yet another plant interface could operate generation systems. 

1. A method for capturing emissions from a fuel combustion process comprising: providing a fuel to a combustor on a gas turbine; providing an oxidant to the combustor; combusting the fuel and the oxidant in the combustor to produce an exhaust gas; passing at least a portion of the exhaust gas to one or more catalyst beds, wherein the one or more catalyst beds: promote a reaction which consumes CO and produces CO₂; and adsorb CO₂; reducing the pressure at the catalyst beds by outputting a blow down stream from the catalyst beds; and purging CO₂ from the one or more catalyst beds with a regenerant stream to create a recovery stream.
 2. The method of claim 1, further comprising cooling and condensing the recovery stream to recover energy and concentrated CO₂.
 3. The method of claim 1, wherein the one or more catalyst beds comprise at least two catalyst beds.
 4. The method of claim 3, further comprising cycling the adsorption of CO₂ by the at least two catalyst beds to allow regeneration of at least one catalyst bed while at least one other bed continues to adsorb CO₂.
 5. The method of claim 1, further comprising passing the product stream to one or more non-catalyst adsorbent beds wherein the one or more non-catalyst adsorbent beds adsorb CO₂.
 6. The method of claim 1, further comprising passing both a second portion of the exhaust stream and the recovery stream to one or more non-catalyst adsorbent beds.
 7. The method of claim 1, wherein the regenerant stream comprises at least one of N₂, steam, or liquid water.
 8. The method of claim 1, wherein the regenerant stream comprises liquid water.
 9. A system for capturing emissions from a fuel combustion process comprising: a combustor on a gas turbine configured to receive fuel and an oxidant; an exhaust gas outlet to release exhaust gas from the combustor; one or more catalyst beds positioned downstream from a portion of the exhaust gas outlet, wherein the one or more catalyst beds: promote a reaction which consumes CO and produces CO₂; adsorb CO₂; and wherein the one or more catalyst beds further comprise: a blow down output feed which outputs a blow down stream to reduce the pressure in the one or more catalyst beds; a first purge input feed which receives regenerant stream; a first purge output feed which outputs a recovery stream for purging CO₂ from the one or more catalyst beds.
 10. The system of claim 9, further comprising a heat exchanger and condenser downstream from the recovery stream to recover energy and concentrated CO₂.
 11. The system of claim 9, wherein the one or more catalyst beds comprise at least two catalyst beds.
 12. The system of claim 11, wherein adsorption of CO₂ by the at least two catalyst beds is cycled to allow regeneration of at least one catalyst bed while at least one other bed continues to adsorb CO₂.
 13. The system of claim 9, further comprising one or more non-catalyst adsorbent beds downstream from the recovery stream wherein the one or more non-catalyst adsorbent beds adsorb CO₂.
 14. The system of claim 9, wherein the regenerant stream comprises at least one of N₂, steam, or liquid water.
 15. The system of claim 9, wherein the regenerant stream comprises liquid water.
 16. A method for capturing emissions from a hydrogen generation fuel combustion process comprising: providing a fuel to a fuel reforming reactor; providing an oxidant to the fuel reforming reactor; combusting the fuel and the oxidant in the fuel reforming reactor to produce an exhaust gas; passing at least a portion of the exhaust gas to one or more catalyst beds, wherein the one or more catalyst beds: promote a reaction which consumes CO and produces CO₂; and adsorb CO₂; reducing the pressure at the catalyst beds by outputting a blow down stream from the catalyst beds; and purging CO₂ from the one or more catalyst beds with a regenerant stream to create a recovery stream; wherein the one or more catalyst beds are configured to operate on a fast cycle on the order of seconds and are connected by rotary or non-rotary valving means.
 17. The method of claim 17, wherein the regenerant stream comprises at least one of N₂, CO₂, steam, or liquid water. 